The interaction is very significant and has been known to occur with even very small amounts of alcohol.

It's not clear why metronidazole and alcohol affect each other, and it's impossible to be sure exactly how long the problem might last after stopping metronidazole. This is because there has been very little research into this.

Manufacturers of metronidazole advise that you should avoid drinking alcohol while taking the antibiotic and for 48 hours after finishing the course. This is because it takes roughly 48 hours for metronidazole to be cleared from the body of an average adult.

During this time, it may be sensible to also avoid alcohol-containing cough and cold remedies and mouthwashes.